/*
 * jmemdos.c
 *
 * Copyright (C) 1992-1994, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file provides an MS-DOS-compatible implementation of the system-
 * dependent portion of the JPEG memory manager.  Temporary data can be
 * stored in extended or expanded memory as well as in regular DOS files.
 *
 * If you use this file, you must be sure that NEED_FAR_POINTERS is defined
 * if you compile in a small-data memory model; it should NOT be defined if
 * you use a large-data memory model.  This file is not recommended if you
 * are using a flat-memory-space 386 environment such as DJGCC or Watcom C.
 * Also, this code will NOT work if struct fields are aligned on greater than
 * 2-byte boundaries.
 *
 * Based on code contributed by Ge' Weijers.
 */

/*
 * If you have both extended and expanded memory, you may want to change the
 * order in which they are tried in jopen_backing_store.  On a 286 machine
 * expanded memory is usually faster, since extended memory access involves
 * an expensive protected-mode-and-back switch.  On 386 and better, extended
 * memory is usually faster.  As distributed, the code tries extended memory
 * first (what? not everyone has a 386? :-).
 *
 * You can disable use of extended/expanded memory entirely by altering these
 * definitions or overriding them from the Makefile (eg, -DEMS_SUPPORTED=0).
 */

#ifndef XMS_SUPPORTED
#define XMS_SUPPORTED  1
#endif
#ifndef EMS_SUPPORTED
#define EMS_SUPPORTED  1
#endif


#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jmemsys.h"     /* import the system-dependent declarations */

#ifndef HAVE_STDLIB_H       /* <stdlib.h> should declare these */
extern void * malloc JPP( (size_t size) );
extern void free JPP( (void * ptr) );
extern char * getenv JPP( (const char * name) );
#endif

#ifdef NEED_FAR_POINTERS

#ifdef __TURBOC__
/* These definitions work for Borland C (Turbo C) */
#include <alloc.h>       /* need farmalloc(), farfree() */
#define far_malloc( x )   farmalloc( x )
#define far_free( x ) farfree( x )
#else
/* These definitions work for Microsoft C and compatible compilers */
#include <malloc.h>      /* need _fmalloc(), _ffree() */
#define far_malloc( x )   _fmalloc( x )
#define far_free( x ) _ffree( x )
#endif

#else /* not NEED_FAR_POINTERS */

#define far_malloc( x )   malloc( x )
#define far_free( x ) free( x )

#endif /* NEED_FAR_POINTERS */

#ifdef DONT_USE_B_MODE      /* define mode parameters for fopen() */
#define READ_BINARY "r"
#else
#define READ_BINARY "rb"
#endif

#if MAX_ALLOC_CHUNK >= 65535L   /* make sure jconfig.h got this right */
MAX_ALLOC_CHUNK should be less than 64 K.  /* deliberate syntax error */
    #endif


/*
 * Declarations for assembly-language support routines (see jmemdosa.asm).
 *
 * The functions are declared "far" as are all pointer arguments;
 * this ensures the assembly source code will work regardless of the
 * compiler memory model.  We assume "short" is 16 bits, "long" is 32.
 */

typedef void far * XMSDRIVER;   /* actually a pointer to code */
typedef struct {        /* registers for calling XMS driver */
    unsigned short ax, dx, bx;
    void far *     ds_si;
} XMScontext;
typedef struct {        /* registers for calling EMS driver */
    unsigned short ax, dx, bx;
    void far *     ds_si;
} EMScontext;

EXTERN short far jdos_open JPP( ( short far * handle, char far * filename ) );
EXTERN short far jdos_close JPP( (short handle) );
EXTERN short far jdos_seek JPP( ( short handle, long offset ) );
EXTERN short far jdos_read JPP( ( short handle, void far * buffer,
                                  unsigned short count ) );
EXTERN short far jdos_write JPP( ( short handle, void far * buffer,
                                   unsigned short count ) );
EXTERN void far jxms_getdriver JPP( (XMSDRIVER far *) );
EXTERN void far jxms_calldriver JPP( ( XMSDRIVER, XMScontext far * ) );
EXTERN short far jems_available JPP( (void) );
EXTERN void far jems_calldriver JPP( (EMScontext far *) );


/*
 * Selection of a file name for a temporary file.
 * This is highly system-dependent, and you may want to customize it.
 */

static int next_file_num;   /* to distinguish among several temp files */

LOCAL void
select_file_name( char * fname ) {
    const char * env;
    char * ptr;
    FILE * tfile;

    /* Keep generating file names till we find one that's not in use */
    for (;; ) {
        /* Get temp directory name from environment TMP or TEMP variable;
         * if none, use "."
         */
        if ( ( env = (const char *) getenv( "TMP" ) ) == NULL ) {
            if ( ( env = (const char *) getenv( "TEMP" ) ) == NULL ) {
                env = ".";
            }
        }
        if ( *env == '\0' ) {/* null string means "." */
            env = ".";
        }
        ptr = fname;    /* copy name to fname */
        while ( *env != '\0' ) {
            *ptr++ = *env++;
        }
        if ( ( ptr[-1] != '\\' ) && ( ptr[-1] != '/' ) ) {
            *ptr++ = '\\';
        }               /* append backslash if not in env variable */
        /* Append a suitable file name */
        next_file_num++;    /* advance counter */
        sprintf( ptr, "JPG%03d.TMP", next_file_num );
        /* Probe to see if file name is already in use */
        if ( ( tfile = fopen( fname, READ_BINARY ) ) == NULL ) {
            break;
        }
        fclose( tfile );/* oops, it's there; close tfile & try again */
    }
}


/*
 * Near-memory allocation and freeing are controlled by the regular library
 * routines malloc() and free().
 */

GLOBAL void *
jpeg_get_small( j_common_ptr cinfo, size_t sizeofobject ) {
    return (void *) malloc( sizeofobject );
}

GLOBAL void
jpeg_free_small( j_common_ptr cinfo, void * object, size_t sizeofobject ) {
    free( object );
}


/*
 * "Large" objects are allocated in far memory, if possible
 */

GLOBAL void FAR *
jpeg_get_large( j_common_ptr cinfo, size_t sizeofobject ) {
    return (void FAR *) far_malloc( sizeofobject );
}

GLOBAL void
jpeg_free_large( j_common_ptr cinfo, void FAR * object, size_t sizeofobject ) {
    far_free( object );
}


/*
 * This routine computes the total memory space available for allocation.
 * It's impossible to do this in a portable way; our current solution is
 * to make the user tell us (with a default value set at compile time).
 * If you can actually get the available space, it's a good idea to subtract
 * a slop factor of 5% or so.
 */

#ifndef DEFAULT_MAX_MEM     /* so can override from makefile */
#define DEFAULT_MAX_MEM     300000L /* for total usage about 450K */
#endif

GLOBAL long
jpeg_mem_available( j_common_ptr cinfo, long min_bytes_needed,
                    long max_bytes_needed, long already_allocated ) {
    return cinfo->mem->max_memory_to_use - already_allocated;
}


/*
 * Backing store (temporary file) management.
 * Backing store objects are only used when the value returned by
 * jpeg_mem_available is less than the total space needed.  You can dispense
 * with these routines if you have plenty of virtual memory; see jmemnobs.c.
 */

/*
 * For MS-DOS we support three types of backing storage:
 *   1. Conventional DOS files.  We access these by direct DOS calls rather
 *      than via the stdio package.  This provides a bit better performance,
 *      but the real reason is that the buffers to be read or written are FAR.
 *      The stdio library for small-data memory models can't cope with that.
 *   2. Extended memory, accessed per the XMS V2.0 specification.
 *   3. Expanded memory, accessed per the LIM/EMS 4.0 specification.
 * You'll need copies of those specs to make sense of the related code.
 * The specs are available by Internet FTP from the SIMTEL archives
 * (oak.oakland.edu and its various mirror sites).  See files
 * pub/msdos/microsoft/xms20.arc and pub/msdos/info/limems41.zip.
 */


/*
 * Access methods for a DOS file.
 */


METHODDEF void
read_file_store( j_common_ptr cinfo, backing_store_ptr info,
                 void FAR * buffer_address,
                 long file_offset, long byte_count ) {
    if ( jdos_seek( info->handle.file_handle, file_offset ) ) {
        ERREXIT( cinfo, JERR_TFILE_SEEK );
    }
    /* Since MAX_ALLOC_CHUNK is less than 64K, byte_count will be too. */
    if ( byte_count > 65535L ) {/* safety check */
        ERREXIT( cinfo, JERR_BAD_ALLOC_CHUNK );
    }
    if ( jdos_read( info->handle.file_handle, buffer_address,
                    (unsigned short) byte_count ) ) {
        ERREXIT( cinfo, JERR_TFILE_READ );
    }
}


METHODDEF void
write_file_store( j_common_ptr cinfo, backing_store_ptr info,
                  void FAR * buffer_address,
                  long file_offset, long byte_count ) {
    if ( jdos_seek( info->handle.file_handle, file_offset ) ) {
        ERREXIT( cinfo, JERR_TFILE_SEEK );
    }
    /* Since MAX_ALLOC_CHUNK is less than 64K, byte_count will be too. */
    if ( byte_count > 65535L ) {/* safety check */
        ERREXIT( cinfo, JERR_BAD_ALLOC_CHUNK );
    }
    if ( jdos_write( info->handle.file_handle, buffer_address,
                     (unsigned short) byte_count ) ) {
        ERREXIT( cinfo, JERR_TFILE_WRITE );
    }
}


METHODDEF void
close_file_store( j_common_ptr cinfo, backing_store_ptr info ) {
    jdos_close( info->handle.file_handle );/* close the file */
    remove( info->temp_name );/* delete the file */
/* If your system doesn't have remove(), try unlink() instead.
 * remove() is the ANSI-standard name for this function, but
 * unlink() was more common in pre-ANSI systems.
 */
    TRACEMSS( cinfo, 1, JTRC_TFILE_CLOSE, info->temp_name );
}


LOCAL boolean
open_file_store( j_common_ptr cinfo, backing_store_ptr info,
                 long total_bytes_needed ) {
    short handle;

    select_file_name( info->temp_name );
    if ( jdos_open( (short far *) &handle, (char far *) info->temp_name ) ) {
        /* might as well exit since jpeg_open_backing_store will fail anyway */
        ERREXITS( cinfo, JERR_TFILE_CREATE, info->temp_name );
        return FALSE;
    }
    info->handle.file_handle = handle;
    info->read_backing_store = read_file_store;
    info->write_backing_store = write_file_store;
    info->close_backing_store = close_file_store;
    TRACEMSS( cinfo, 1, JTRC_TFILE_OPEN, info->temp_name );
    return TRUE;        /* succeeded */
}


/*
 * Access methods for extended memory.
 */

#if XMS_SUPPORTED

static XMSDRIVER xms_driver;    /* saved address of XMS driver */

typedef union {         /* either long offset or real-mode pointer */
    long       offset;
    void far * ptr;
} XMSPTR;

typedef struct {        /* XMS move specification structure */
    long   length;
    XMSH   src_handle;
    XMSPTR src;
    XMSH   dst_handle;
    XMSPTR dst;
} XMSspec;

#define ODD( X )  ( ( ( X ) & 1L ) != 0 )


METHODDEF void
read_xms_store( j_common_ptr cinfo, backing_store_ptr info,
                void FAR * buffer_address,
                long file_offset, long byte_count ) {
    XMScontext ctx;
    XMSspec spec;
    char endbuffer[2];

    /* The XMS driver can't cope with an odd length, so handle the last byte
     * specially if byte_count is odd.  We don't expect this to be common.
     */

    spec.length = byte_count & ( ~1L );
    spec.src_handle = info->handle.xms_handle;
    spec.src.offset = file_offset;
    spec.dst_handle = 0;
    spec.dst.ptr = buffer_address;

    ctx.ds_si = (void far *) &spec;
    ctx.ax = 0x0b00;    /* EMB move */
    jxms_calldriver( xms_driver, (XMScontext far *) &ctx );
    if ( ctx.ax != 1 ) {
        ERREXIT( cinfo, JERR_XMS_READ );
    }

    if ( ODD( byte_count ) ) {
        read_xms_store( cinfo, info, (void FAR *) endbuffer,
                        file_offset + byte_count - 1L, 2L );
        ( (char FAR *) buffer_address )[byte_count - 1L] = endbuffer[0];
    }
}


METHODDEF void
write_xms_store( j_common_ptr cinfo, backing_store_ptr info,
                 void FAR * buffer_address,
                 long file_offset, long byte_count ) {
    XMScontext ctx;
    XMSspec spec;
    char endbuffer[2];

    /* The XMS driver can't cope with an odd length, so handle the last byte
     * specially if byte_count is odd.  We don't expect this to be common.
     */

    spec.length = byte_count & ( ~1L );
    spec.src_handle = 0;
    spec.src.ptr = buffer_address;
    spec.dst_handle = info->handle.xms_handle;
    spec.dst.offset = file_offset;

    ctx.ds_si = (void far *) &spec;
    ctx.ax = 0x0b00;    /* EMB move */
    jxms_calldriver( xms_driver, (XMScontext far *) &ctx );
    if ( ctx.ax != 1 ) {
        ERREXIT( cinfo, JERR_XMS_WRITE );
    }

    if ( ODD( byte_count ) ) {
        read_xms_store( cinfo, info, (void FAR *) endbuffer,
                        file_offset + byte_count - 1L, 2L );
        endbuffer[0] = ( (char FAR *) buffer_address )[byte_count - 1L];
        write_xms_store( cinfo, info, (void FAR *) endbuffer,
                         file_offset + byte_count - 1L, 2L );
    }
}


METHODDEF void
close_xms_store( j_common_ptr cinfo, backing_store_ptr info ) {
    XMScontext ctx;

    ctx.dx = info->handle.xms_handle;
    ctx.ax = 0x0a00;
    jxms_calldriver( xms_driver, (XMScontext far *) &ctx );
    TRACEMS1( cinfo, 1, JTRC_XMS_CLOSE, info->handle.xms_handle );
    /* we ignore any error return from the driver */
}


LOCAL boolean
open_xms_store( j_common_ptr cinfo, backing_store_ptr info,
                long total_bytes_needed ) {
    XMScontext ctx;

    /* Get address of XMS driver */
    jxms_getdriver( (XMSDRIVER far *) &xms_driver );
    if ( xms_driver == NULL ) {
        return FALSE;
    }                   /* no driver to be had */

    /* Get version number, must be >= 2.00 */
    ctx.ax = 0x0000;
    jxms_calldriver( xms_driver, (XMScontext far *) &ctx );
    if ( ctx.ax < (unsigned short) 0x0200 ) {
        return FALSE;
    }

    /* Try to get space (expressed in kilobytes) */
    ctx.dx = (unsigned short) ( ( total_bytes_needed + 1023L ) >> 10 );
    ctx.ax = 0x0900;
    jxms_calldriver( xms_driver, (XMScontext far *) &ctx );
    if ( ctx.ax != 1 ) {
        return FALSE;
    }

    /* Succeeded, save the handle and away we go */
    info->handle.xms_handle = ctx.dx;
    info->read_backing_store = read_xms_store;
    info->write_backing_store = write_xms_store;
    info->close_backing_store = close_xms_store;
    TRACEMS1( cinfo, 1, JTRC_XMS_OPEN, ctx.dx );
    return TRUE;        /* succeeded */
}

#endif /* XMS_SUPPORTED */


/*
 * Access methods for expanded memory.
 */

#if EMS_SUPPORTED

/* The EMS move specification structure requires word and long fields aligned
 * at odd byte boundaries.  Some compilers will align struct fields at even
 * byte boundaries.  While it's usually possible to force byte alignment,
 * that causes an overall performance penalty and may pose problems in merging
 * JPEG into a larger application.  Instead we accept some rather dirty code
 * here.  Note this code would fail if the hardware did not allow odd-byte
 * word & long accesses, but all 80x86 CPUs do.
 */

typedef void far * EMSPTR;

typedef union {         /* EMS move specification structure */
    long length;        /* It's easy to access first 4 bytes */
    char bytes[18];     /* Misaligned fields in here! */
} EMSspec;

/* Macros for accessing misaligned fields */
#define FIELD_AT( spec, offset, type )  ( *( (type *) &( spec.bytes[offset] ) ) )
#define SRC_TYPE( spec )      FIELD_AT( spec, 4, char )
#define SRC_HANDLE( spec )    FIELD_AT( spec, 5, EMSH )
#define SRC_OFFSET( spec )    FIELD_AT( spec, 7, unsigned short )
#define SRC_PAGE( spec )      FIELD_AT( spec, 9, unsigned short )
#define SRC_PTR( spec )       FIELD_AT( spec, 7, EMSPTR )
#define DST_TYPE( spec )      FIELD_AT( spec, 11, char )
#define DST_HANDLE( spec )    FIELD_AT( spec, 12, EMSH )
#define DST_OFFSET( spec )    FIELD_AT( spec, 14, unsigned short )
#define DST_PAGE( spec )      FIELD_AT( spec, 16, unsigned short )
#define DST_PTR( spec )       FIELD_AT( spec, 14, EMSPTR )

#define EMSPAGESIZE 16384L  /* gospel, see the EMS specs */

#define HIBYTE( W )  ( ( ( W ) >> 8 ) & 0xFF )
#define LOBYTE( W )  ( ( W ) & 0xFF )


METHODDEF void
read_ems_store( j_common_ptr cinfo, backing_store_ptr info,
                void FAR * buffer_address,
                long file_offset, long byte_count ) {
    EMScontext ctx;
    EMSspec spec;

    spec.length = byte_count;
    SRC_TYPE( spec ) = 1;
    SRC_HANDLE( spec ) = info->handle.ems_handle;
    SRC_PAGE( spec )   = (unsigned short) ( file_offset / EMSPAGESIZE );
    SRC_OFFSET( spec ) = (unsigned short) ( file_offset % EMSPAGESIZE );
    DST_TYPE( spec ) = 0;
    DST_HANDLE( spec ) = 0;
    DST_PTR( spec )    = buffer_address;

    ctx.ds_si = (void far *) &spec;
    ctx.ax = 0x5700;    /* move memory region */
    jems_calldriver( (EMScontext far *) &ctx );
    if ( HIBYTE( ctx.ax ) != 0 ) {
        ERREXIT( cinfo, JERR_EMS_READ );
    }
}


METHODDEF void
write_ems_store( j_common_ptr cinfo, backing_store_ptr info,
                 void FAR * buffer_address,
                 long file_offset, long byte_count ) {
    EMScontext ctx;
    EMSspec spec;

    spec.length = byte_count;
    SRC_TYPE( spec ) = 0;
    SRC_HANDLE( spec ) = 0;
    SRC_PTR( spec )    = buffer_address;
    DST_TYPE( spec ) = 1;
    DST_HANDLE( spec ) = info->handle.ems_handle;
    DST_PAGE( spec )   = (unsigned short) ( file_offset / EMSPAGESIZE );
    DST_OFFSET( spec ) = (unsigned short) ( file_offset % EMSPAGESIZE );

    ctx.ds_si = (void far *) &spec;
    ctx.ax = 0x5700;    /* move memory region */
    jems_calldriver( (EMScontext far *) &ctx );
    if ( HIBYTE( ctx.ax ) != 0 ) {
        ERREXIT( cinfo, JERR_EMS_WRITE );
    }
}


METHODDEF void
close_ems_store( j_common_ptr cinfo, backing_store_ptr info ) {
    EMScontext ctx;

    ctx.ax = 0x4500;
    ctx.dx = info->handle.ems_handle;
    jems_calldriver( (EMScontext far *) &ctx );
    TRACEMS1( cinfo, 1, JTRC_EMS_CLOSE, info->handle.ems_handle );
    /* we ignore any error return from the driver */
}


LOCAL boolean
open_ems_store( j_common_ptr cinfo, backing_store_ptr info,
                long total_bytes_needed ) {
    EMScontext ctx;

    /* Is EMS driver there? */
    if ( !jems_available() ) {
        return FALSE;
    }

    /* Get status, make sure EMS is OK */
    ctx.ax = 0x4000;
    jems_calldriver( (EMScontext far *) &ctx );
    if ( HIBYTE( ctx.ax ) != 0 ) {
        return FALSE;
    }

    /* Get version, must be >= 4.0 */
    ctx.ax = 0x4600;
    jems_calldriver( (EMScontext far *) &ctx );
    if ( ( HIBYTE( ctx.ax ) != 0 ) || ( LOBYTE( ctx.ax ) < 0x40 ) ) {
        return FALSE;
    }

    /* Try to allocate requested space */
    ctx.ax = 0x4300;
    ctx.bx = (unsigned short) ( ( total_bytes_needed + EMSPAGESIZE - 1L ) / EMSPAGESIZE );
    jems_calldriver( (EMScontext far *) &ctx );
    if ( HIBYTE( ctx.ax ) != 0 ) {
        return FALSE;
    }

    /* Succeeded, save the handle and away we go */
    info->handle.ems_handle = ctx.dx;
    info->read_backing_store = read_ems_store;
    info->write_backing_store = write_ems_store;
    info->close_backing_store = close_ems_store;
    TRACEMS1( cinfo, 1, JTRC_EMS_OPEN, ctx.dx );
    return TRUE;        /* succeeded */
}

#endif /* EMS_SUPPORTED */


/*
 * Initial opening of a backing-store object.
 */

GLOBAL void
jpeg_open_backing_store( j_common_ptr cinfo, backing_store_ptr info,
                         long total_bytes_needed ) {
    /* Try extended memory, then expanded memory, then regular file. */
#if XMS_SUPPORTED
    if ( open_xms_store( cinfo, info, total_bytes_needed ) ) {
        return;
    }
#endif
#if EMS_SUPPORTED
    if ( open_ems_store( cinfo, info, total_bytes_needed ) ) {
        return;
    }
#endif
    if ( open_file_store( cinfo, info, total_bytes_needed ) ) {
        return;
    }
    ERREXITS( cinfo, JERR_TFILE_CREATE, "" );
}


/*
 * These routines take care of any system-dependent initialization and
 * cleanup required.
 */

GLOBAL long
jpeg_mem_init( j_common_ptr cinfo ) {
    next_file_num = 0;      /* initialize temp file name generator */
    return DEFAULT_MAX_MEM; /* default for max_memory_to_use */
}

GLOBAL void
jpeg_mem_term( j_common_ptr cinfo ) {
    /* Microsoft C, at least in v6.00A, will not successfully reclaim freed
     * blocks of size > 32Kbytes unless we give it a kick in the rear, like so:
     */
#ifdef NEED_FHEAPMIN
    _fheapmin();
#endif
}
